RAW is like a negative in some ways, the ajustments you make and non-distructive, you can make some ajustments and open the image, then 6 months later you can go back and make a totally different set of ajustments to your original RAW, it's just as you left it last time, none of the ajustments damage or degrade it in any way.
I don't work from a copy of RAW, theres no need, but I do make copies for safety, these are on external drives and DVD, purely as a back-up in case the computer keels over.
Wayne